Frost dates for Port Of Morgan, MT
At Port Of Morgan, the median last spring frost (32°F) is May 19 and the median first fall frost is Sep 22, for a typical growing season of 124 days. For a 90% chance that the last frost has passed, wait until Jun 2. Nearby ZIP codes are in USDA hardiness zone 3b.
- May 19Last spring frost (median)50% chance of 32°F after this date
- Jun 2Safer planting date10% chance of 32°F after this date
- Sep 22First fall frost (median)50% chance of 32°F by this date
- 124 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 18 | May 31 | Jun 15 |
| 32°F | May 5 | May 19 | Jun 2 |
| 28°F | Apr 23 | May 8 | May 21 |
| 24°F | Apr 10 | Apr 27 | May 11 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Aug 30 | Sep 12 | Sep 24 |
| 32°F | Sep 9 | Sep 22 | Oct 4 |
| 28°F | Sep 15 | Sep 30 | Oct 12 |
| 24°F | Sep 24 | Oct 8 | Oct 23 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 83 days | 103 days | 121 days |
| 32°F | 105 days | 124 days | 142 days |
| 28°F | 124 days | 144 days | 164 days |
| 24°F | 143 days | 164 days | 185 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59537 | 3b | -35 to -30°F | 21 km |
| 59544 | 3b | -35 to -30°F | 30 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00246672, at 48.9978, -107.8331, elevation 863 m (2,830 ft).
- Data quality: Representative (10+ years), 27 years of freeze data.
- Average days per year at or below 32°F: 189.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Turner 11n (41 km)
- Malta 7 E (68 km)
- Saco 1 NNW (69 km)
- Malta (71 km)
- Harlem (87 km)
- Hinsdale 4 SW (88 km)
- Fort Belknap 2 SW (91 km)
- Content 4 NNE (105 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.